Cross-sections for hadronic and leptonic two-fermion events, and leptonic forward-backward asymmetries, have been measured in e
+e
− collisions at a centre-of-mass energy of 161 GeV, using the OPAL ...detector at LEP. Results are presented both including and excluding the dominant production of radiative γZ
0 events. We have measured
R
b, the ratio of the number of b
b
to all multihadronic events at 161 GeV, and compared it to the result obtained at 130–136 GeV. All results agree well with the Standard Model expectations. In a model-independent fit to the Z
0 lineshape, the data presented here give an improved precision on the γZ
0-interference term. The data have also been used to obtain new limits on extensions of the Standard Model described by effective four-fermion contact interactions.
A search for scalar particles and neutralinos such as those predicted by supersymmetric models has been performed using a data sample of 4.4 million hadronic Z
0 decays recorded by the OPAL detector ...at the e
+e
− collider LEP. The production of such particles typically leads to event topologies consisting of an acoplanar pair of jets, or of a mono-jet, accompanied by sizeable missing energy owing to neutrinos and other undetectable neutral particles. Limits are obtained, at the 95% confidence level, on the masses and production rates of scalar particles produced in association with the Z
0. Limits are also placed on neutralino production, for which an additional possible signature is also studied, events containing a single observed photon. Within the Minimal Supersymmetric Standard Model, the mass of the lightest neutralino is found to be larger than 12.5 GeV/
c
2
at 95% C.L., provided that tan β is larger than 1.5.
A new measurement of the τ lifetime is presented. It uses data collected with the
Opal detector during 1994, which almost doubles the size of the
Opal τ sample. Two statistically independent ...techniques are used: an impact parameter analysis of one-prong decay tracks and a fit to the decay length distribution of three-prong decays. The lifetime obtained from the 1994 data by combining the results of these methods is
τ
τ
= 289.7 ± 2.5 (stat)± 1.5 (sys) fs. When combined with the previous
Opal τ lifetime measurement the improved τ lifetime is
τ
τ
= 289.2 ± 1.7 (stat.) ± 1.2 (sys.) fs.
Squeezed states of light have been recently used to improve the sensitivity of laser interferometric gravitational-wave detectors beyond the quantum limit. To completely establish quantum engineering ...as a realistic option for the next generation of detectors, it is crucial to study and quantify the noise coupling mechanisms which injection of squeezed states could potentially introduce. We present a direct measurement of the impact of backscattered light from a squeezed-light source deployed on one of the 4 km long detectors of the Laser Interferometric Gravitational Wave Observatory (LIGO). We also show how our measurements inform the design of squeezed light sources compatible with the even more sensitive advanced detectors currently under construction, such as Advanced LIGO.
Background-free, quasi-monoenergetic electron beams from a self-injected laser wakefield accelerator Banerjee, S.; Kalmykov, S.; Powers, N. ...
2011 International Quantum Electronics Conference (IQEC) and Conference on Lasers and Electro-Optics (CLEO) Pacific Rim incorporating the Australasian Conference on Optics, Lasers and Spectroscopy and the Australian Conference on Optical Fibre Technology,
2011-Aug.
Conference Proceeding
Odprti dostop
Stable 200-400-MeV quasi-monoenergetic electron bunches (ΔE/E<;10%), ~ 10-pC charge, and no dark-current are produced when a self-injected laser plasma accelerator is optimized. PIC simulations ...demonstrate these beams are produced near the threshold for self-injection.
A search is described to detect charged Higgs bosons via the process Z
0 → H
+H
−, using data collected by the OPAL detector at LEP which correspond to an integrated luminosity of approximately 110 ...pb
−1. It is assumed that the H
+ boson decays only to
τ
+
ν
τ
and c
s
final states. From the negative outcome of this search a lower bound of 44.1 GeV (95% CL) is derived for the mass of the charged Higgs boson.
We have searched for decays of the
τ lepton into seven or more charged particles, using data collected with the OPAL detector from 1990 to 1995 in e
+e
− collisions at √8 ≈ M
z
. No candidate events ...were found and an upper limit on the branching ratio for
τ decays into seven charged particles of 1.8 × 10
−5 at the 95% confidence level was determined.
6
References in this paper to specific charge states apply to the charge conjugate states as well.
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